CIS 101: Computer Programming and Problem Solving Lecture 4 Usman Roshan Department of Computer Science NJIT

Overview So far we have seen how to define basic mathematical expressions and how to manipulate arrays and matrices Now we will look at script files and functions. They are useful for storing sets of commands and defining them apriori. Also an important step before we get into programming with control and flow operators Today: chapters 4 and 6

Scripts Used for writing programs Script variables are global. They can be accessed and modified from anywhere

Creating scripts

Editor for scripts

Running script

Output of script

Script for mean of three numbers

Output of mean script

fprintf command A powerful command General syntax fprintf(‘text as string %-5.2f additional text’, variable name) Formatting elements

Updated mean script

Output of updated mean script

Writing to a file fid = fopen(‘file_name’, ‘permission’) File permissions –r = open for reading –w = open for writing (if file exists then content is deleted) –a = open for appending

Mean script output to file

Output file of mean script

Function files Function File Input data Output

Function syntax function [output arguments] = function_name(input arguments) Example functions: function [A] = RectArea(x, y) function [V, S] = SphereVolArea(r)

Local and global variables So far ALL variables we have worked with have been global. This means they can be accessed and modified by any part of the program In functions variables are local by default (and global if they are defined as such)

Memory space Global memory space accessible by all scripts and functions Local space for function A Local space for function B

Defining and calling a function A function file must be saved before it can be used. The name of the file must be the same as the function name Examples: –FunctionFilename –function [A] = RectArea(x,y)RecArea.m –function[V, S] = SphereVolArea(r) SphereVolArea.m

Function for computing area of sphere

Area of sphere It won’t run if you click on the run button

Area of sphere The function is called from the command line…

Area of sphere Or the function can be called from a script.

Area of sphere Function output from script

Comparison between functions and scripts Both scripts and funtion files are saved with.m extension The first line in a function file is the definition line Function variables are local whereas script ones are global Function files can accept data through input arguments and can return data similarly When a function file is saved, the name of the file should be the same as the function’s.

Inline functions name = inline(‘math expression typed as a string’) name = inline(‘math expression’, arg1, …, argn) For example, double = inline(‘2*x’) defines a function that doubles the input. So double(10) = 20

Using inline to define area of sphere